If he is just grooming it a lot, don't be too worried. If it starts to look irritated due to scratching/grooming, i would just see if the vet could do a check-up. Look for changes in his behavior and if there are non, don't stress yourself out. If he seems normal and acting like himself, he should be fine. Just keep an eye on him.
The sore is gone, or is just the itching better?
Anyway, check his genitals for sores too. If the sores persist, return or spread I would see a vet, could be rabbit syphilis. Or some fungal infection. All treatable.